P3020 Battery block 10 gets weak

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Priorrides, Nov 18, 2025 at 5:52 PM.

  1. Priorrides

    Priorrides New Member

    Joined:
    May 27, 2025
    3
    0
    0
    Location:
    Usa
    Vehicle:
    2012 Prius
    Model:
    N/A
    Working on a friends 2012. He bought this car with a bad ABS unit and it took us several months to replace it. Prior to the ABS repair the car had no battery codes and would operate in EV mode, now it constantly runs and won't go into EV mode. Now that we finally replaced the ABS unit, scanning shows:

    Current P3020 Battery Block 10 gets weak

    Pending P0A7F Deterioration of hybrid battery pack

    Pending P0A80 Replacement of hybrid battery pack

    The ABS/VSC/TRAC shows:

    Current C1259 Regenerative malfunction of HV control system

    Current C1310 Malfunction of HV system

    I think this car ultimately needs a battery replacement, but I was wondering what should I do/check before he goes and shells out a bunch more money for a battery.

    I'm thinking I should check for corrosion/damage in the voltage sensor ECU. Check for corrosion on the bus bars. And maybe try to equalize the cell voltage??? I can do all that for little to no cost. But, I don't know if its worth spending money on multichannel hobby chargers to try and fully recondition an old battery. Maybe I should also check and see if there is a date on the battery to see if its ever been replaced?

    Any opinions, tips or advice is appreciated.
     
    #1 Priorrides, Nov 18, 2025 at 5:52 PM
  2. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    12,677
    5,117
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    When an old battery pack sits unused for a long time the cells of NiMH in particular have a peculiar problem with self-discharging at different rates. To address this you need a high voltage trickle charger to recharge and balance the pack by sending between 250V to 350V DC at 1/3 of an amp for 24 hours and problem is solved.
     
    #2 PriusCamper, Nov 19, 2025 at 2:06 AM
  3. Priorrides

    Priorrides New Member

    Joined:
    May 27, 2025
    3
    0
    0
    Location:
    Usa
    Vehicle:
    2012 Prius
    Model:
    N/A
    Would just balancing the packs work? I mean, disassemble battery, align cells so all positives are on one side, all negative on the other and connect them via a wire or bus bar and let the voltage balance. I realize this is not ideal, best way *seems* to be balancing via a multichannel hobby charger. I have not heard of your method, do you have any further info, links or just keywords to use in a search so I can look deeper? Thanks.
     
    #3 Priorrides, Nov 19, 2025 at 1:15 PM
  4. indel

    indel Junior Member

    Joined:
    Apr 1, 2024
    43
    17
    0
    Location:
    Northwest Indiana
    Vehicle:
    2012 Prius
    Model:
    Two
    That's interesting. I recently bought a 2012 Prius and all the information I have suggests it sat for a few months on dealer lots. I have documented my battery tests using Dr. Prius in another thread. Now I am wondering if my problem is similar to what you are describing. How does one trickle charge a battery? What equipment is needed?
     
    #4 indel, Nov 19, 2025 at 1:36 PM
  5. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    12,677
    5,117
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    Maxx Volts and Hybrid Automotive sells consumer products that are a bit expensive. Or you can build one for: Build Hybrid Battery Maintenance Gear For Under $100 | PriusChat Or even easier see the last posts in that link for the multi-purpose one you can buy online. As for how to install it and how to use it, the install instructions/explanations on Hybrid Automotive's website works great: FAQ - Hybrid Automotive
     
    #5 PriusCamper, Nov 19, 2025 at 2:19 PM
    Priorrides and Brian1954 like this.
  6. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    12,677
    5,117
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    It depends on how much total charge you have left in the pack. If you're battery doesn't have enough charge to start the engine then no that won't work.

    And yes, some people indeed use that method... But each chemistry has a different balancing requirement. Lithium for example is "balanced from below" which is done just as you described, but at the bottom off the discharge curve right before voltage in each cell suddenly drops to 0.0v

    Whereas NiMH is "balanced from above" where by you send a 1/3rd of an amp charge into all 168 cells in a series that's greater than total voltage of the pack and once each cell is full and can't hold anymore it will dissipate that 1/3rd of amp charge as heat, which is why you need the cooling fan to help blow away that excess charge.
     
    #6 PriusCamper, Nov 19, 2025 at 7:53 PM
    Priorrides likes this.
  7. Brian1954

    Brian1954 Senior Member

    Joined:
    Jan 31, 2021
    2,137
    828
    0
    Location:
    South Central PA, USA
    Vehicle:
    2011 Prius
    Model:
    III
    What you described is equalizing the voltage in the battery modules. That is not balancing the battery pack. Balancing is done by using a grid charger for about 20 to 24 hours, as described in post #6.

    FYI, the battery pack is made up of 28 battery modules. Each of those modules has 6 battery cells (1.2v nominal) inside wired in series. All 28 modules are connected in series. So, the complete battery pack consists of 168 cells, wired in series.
     
    #7 Brian1954, Nov 19, 2025 at 8:21 PM
    Last edited: Nov 19, 2025 at 8:36 PM
    PriusCamper likes this.
(You must log in or sign up to post here.)